Strain-Adaptive Liquid Metal Interfaces Overcome Poisson's Ratio Constraints in Piezoresistive Sensors for Infant Sleep Monitoring

Conventional porous piezoresistive sensors suffer from lateral expansion due to a positive Poisson's ratio, causing conductive network fracture and unreliable signals. Existing structural solutions are limited by high costs and poor durability. This study introduces a dynamic conductive interface mechanism using liquid metal (LM) ink to bypass Poisson's ratio limitations. By coating eutectic gallium-indium (EGaIn) onto a hydrophilic porous thermoplastic polyurethane (TPU) scaffold, a strain-adaptive conductive layer is constructed, where LM droplets directionally flow to fill microcracks during deformation. This mechanism retains 98.73% of initial conductive pathways under 98% tensile strain, achieving ultra-high sensitivity (693.65 kPa⁻¹, 0.32-10.24 kPa). The LM-based sensor demonstrates intrinsic antibacterial properties and launderability. Integrated into an intelligent infant pillow with a 16-chanels sensor array, the system enables real-time cephalic pressure monitoring and edge-computed posture correction via a companion app. This work proposes a material-mechanics co-design strategy to overcome Poisson ratio constraints, advancing high-performance, scalable wearable biomedical devices.